Hi. I love your message board! 

I live in Nicaragua and have just bought a 22 square meter lot on which I plan to build a 3 bdrm house. I have dug a 4 foot square pit about 12 feet deep for a temporary outhoues for the builders. The upper half is lined with cement block and morter. The lower half is just firm dark dirt, well below the layer of hard clay-like substrata. Looks like really nice drainage. 

After the builders are gone, I would like to turn this pit into a drywell for the washing machine, showers and sink water, leaving my 1100 liter septic tank for just the three toilets (three adults and one child in the house).

Do you think I could fill the bottom half of this pit with a layer of gravel on the absolute bottom, sand in the middle bottom and gravel on the top (all of this on the bottom half of the pit where there is no cement block lining)? And then might it be a good idea to have a few moderate drainage pipes in gravel trenches with an outlet pipe coming out a few feet down from the top of the pit in case the water were to rise up that high before draining down below?

My idea is to have the water go into this pit but not melt away the bottom-half sides of the pit, which might prompt the top half of cement blocks to go tumbing down to the bottom half and the whole thing to cave in. I am thinking that the gravel/sand/gravel layer on those bottom 6 feet could add some support and filter out some of the soaps and bacterias from the wash water before it seeps further down. But now after reading each and every one of the entries in the message board, I am worrying about an anaerobic situation in the bottom of the pit, all covered up by gravel/sand and inaccesable.

We have no city sewer system near our land. We have excellent drainage here. There is no drinking water source nearby to worry about. We are not near a lake or stream. There is no flooding. Our lot gently slopes downward away from the pit.

I hope I have given you enough information. Thanks in advance.

Alixe Huete
Managua, Nicaragua
(Central America!)